Manufacture of viscose



Patented Dec. 22, 1936 UNITED STATES PATENT OFFICE,

MANUFACTURE OF VISCOSE Main, Germany No Drawing. Application April 10, 1934, Serial No. 719,969. In Germany April 20, 1933 73 Claims. (01. 260-100) Our present invention relates to the manufacture of artificial articles such as artificial threads, sheets, ribbons from cellulose.

One of its objects is to provide an improved process for the manufacture of artificial articles which is efficient and involves a considerable reduction of costs. Further objects will be seen from the detailed specification following hereafter.

The process according to this invention does not start as usual from dried sheets of sulfite pulp, but from a highly viscous cellulose as obtained according to one of the known processes for disintegrating cellulose-containing materials by means of nitric acid and still contains water from its manufacture. According to the invention, this highly viscous material is converted into alkali-cellulose by the action of caustic alkali and the viscosity of the material is reduced, particularly by the action of an alkali sulfide and gases containing oxygen. The alkali-cellulose is mixed with carbon disulfide and dissolved so as to form viscose containing more than 5 per cent of cellulose; this viscose is spun in known 25 manner into artificial silk, sheets, ribbons and the like. The whole process from the digestion of the wood to the spinning of artificial silk is performed in a very short time and with the con sumption of very small quantities of chemicals.

30 If, for preserving the alpha-cellulose, wood is digested in known manner with small amounts of nitric acid or with nitrogen oxides and air, for instance according to U. S. patents Nos. 1,736,080 and 1,840,198, a cellulose is obtained which even 5 after it has been bleached in the usual way is still highly viscous and is very well suited as a starting material for the manufacture of artificial silk and yields a bright silk even when the alkalicellulose has not been ripened. Since'the diges- 40 tion by means of nitric acid dispenses with the application of pressure vessels, it may be carried through with advantage also when starting from smaller batches and therefore, it is the very process to be used in direct connection with the manu- 45 facture of artificial silk. In the process of digesting wood by using nitric acid the great difficulty, experienced in the sulfite process, namely removal of the waste liquors, exists in a much lower degree. It becomes possible, therefore, to

50 perform the digestion of wood even in those artificial silk factories which are not favorably situated for removal of waste liquors. Furthermore, the combination of the production of the pulp by the nitric acid process with the manufacture of 55 the artificial silk is of a great technical value for the reason that this digestion process requires considerable amounts of alkaline liquors for dissolving the non-cellulose constituents rendered soluble by the nitric acid and that alkaline liquors suitable for this purpose are obtained in large 5 quantities from the mercerization of the cellulose in making the viscose.

Due to its high viscosity and its high degree of whiteness the cellulose digested by means of nitric acid is particularly suited for the manufac- 10 ture of solid and purelywhite artificial silk. According to the invention the high viscosities may be reduced Without difficulty within a short time and indeed with avoidance of tedious intermediate operations, such as dipping, ripening, etc. 15 For reducing the viscosity of the pulp, an alkali sulfide is used the effect of which, as has been found, is enhanced to an extent hitherto unknown, by the infiuence of a gas containing oxygen, for instance air. This operation is accompanied by a strong development of heat. Instead of an alkali sulfide there may also be employed a polysulfide or any other substance having the same effect. The treatment with air of the alkali cellulose containing alkali sulfide is preferably performed directly after centrifuging the alkali cellulose or draining it. The alkali-cellulose may also be treated with air containing hydrogen sulfide, the formation of the sodium sulfide and the action of this substance on the alkali cellulose in the presence of air occurring simultaneously or in succession. The proportion of the alkali sulfide is adjusted to that required for the desired reduction of viscosity. In the finished alkali cellulose the alkali sulfide added should be consumed practically completely. By this mode of operation it is possible to reduce the viscosity of a cellulose having a copper viscosity, for instance, of 400 to within three hours. This is to be contrasted with the usual time necessary for the 40 ripening of the alkali cellulose, namely at least 6 days.

When in this process centrifuges or suction filters are used it is not necessary to specially comminute the alkali cellulose. Of course, the treatment of the alkali-cellulose containing an alkali sulfide may be performed if required also while reducing the alkali-cellulose to fibres or also when comminuting the material in the xanthogenating machine prior to the treatment with carbon bisulfide.

Highly viscous celluloses according to the invention are such as have a copper viscosity higher than 200". By the process of digesting with nitric acid, however, there may be obtained celluloses having a copper viscosity of 1000". These celluloses, too, may be utilized for the manufacture in a. continuous operation of spinning solutions having a low viscosity.

The copper viscosity is determined, without the access of atmospheric oxygen, by measuring the time of flow of a copper oxide-ammonia solution containing 1 per cent of cellulose and accurately adjusted to 20 per cent of NH3 and 1.3 per cent of Cu. The time during which 50 cc.

- of cellulose-copper oxide-ammonia solution flows at 20 0., through the capillary orifice of a viscosimeter represents an exact measurement of the viscosity of the cellulosic material. The viscosimeter is standardized with water and so adjusted that a period of 10 seconds is required for the flow of the water.

The following example illustrates the invention.

Conifer wood or deciduous wood is disintegrated with nitric acid according to one of the known processes. The non-cellulosic constituents rendered soluble by the nitric acid are then extracted by treatment with waste liquor containing alkali sulfide obtained in the mercerization of the preceding batch of cellulose, and the cellulose pulp thus obtained, after previous chlorination for extracting the last remnants of ligneous matter is bleached in the usual manner. The cellulose thus prepared has a copper viscosity of about 350 to 1000", according to the kind of wood employed and according to the digestion process adopted. The bleached material, which by centrifuging and draining has been brought to a dry weight of 20 to 35% is treated with a caustic soda solution of such a strength that inclusive. of the moisture of the material the final concentration amounts to 12 to 18 per cent by volume of NaOH and 10 to 4 per cent by volume of NazS. The. amount of cellulose in the soaking liquor amounts to about 5 per cent by volume. After the mass has been stirred for 2 hours it is centrifuged for about 3 hours until it has three times the weight of the cellulose. During the centrifuging the viscosity due to the action of the atmospheric oxygen, is reduced to about 45", the temperature rising from 20 to 30 to 40 C.

The alkali cellulose thus obtained is then comminuted for a short time in the kneader of a xanthating machine and sulfided in the same apparatus by means of 25 per cent by volume of carbon bisulfide added within 1 hours. The temperature is preferably not allowed to exceed 30 C. The finished cellulose xanthate is finally dissolved by means of a dilute caustic soda solution to form a viscose containing 7.5 per cent of cellulose and 6.5 per cent of alkali. The viscose obtained by this process is clearer than the ordinary viscose obtained from sulfite pulp, so that artificial threads with fine individual titers (indi vidual titer equal to 1 or lower) may easily be produced.

60 hours after dissolution the filtered viscose is spun in the usual manner into a bath at a temperature of 50 0., containing 13 per cent of sulfuric acid and 28 per cent of sodium sulfate.

The artificial silk obtained after being desulfurized in the usual way, is bright and of a pure White, without application of the usual bleaching operation with hypochlorite or baths containing hydrogen peroxide. The silk has a tensile strength of 150 to 160 gr. per 100 deniers, and an extensibility of 20 per cent. When varying the spinning conditions particularly when adopting spinning baths having a high concentration of acid, artificial silk may be obtained having a tensile strength of 200 and 300 gr. and more per 100 deniers.

What we claim is:

1. A process of manufacturing viscose which comprises subjecting wood to digestion with nitric acid, removing the soluble non-cellulosic substances by means of a solution of caustic alkali, washing the cellulose pulp, reducing the content of water of the pulp by mechanical means to to per cent, converting the wet cellulose into alkali cellulose by the addition of a solution of caustic alkali, subjecting the alkali cellulose to the action of an oxygen-containing gas and a viscosity-reducing material selected from the group consisting of alkali sulfides, hydrogen sulfide and alkali polysulfides, converting the alkali cellulose into cellulose xanthate and dissolving said xanthate to form a viscose solution.

2. A process of manufacturing viscose which comprises subjecting wood to digestion with nitric acid, removing the soluble non-cellulosic sub stances by means of a solution of caustic alkali, washing the cellulose pulp, reducing the content of water of the pulp by mechanical means to 65 to 80 per cent, converting the wet cellulose into alkali cellulose by the addition of a solution'of caustic alkali, subjecting the alkali cellulose to the action of alkali sulfide and an oxygen-containing gas, converting the alkali cellulose into cellulose xanthate, and dissolving said xanthate to form a viscose solution.

3. A process of manufacturing viscose which comprises subjecting wood to digestion with nitric acid, removing the soluble non -cellulosic substances by means of a solution of caustic alkali, washing the cellulose pulp reducing the content of water of the pulp by mechanical meansto 65 to 80 per cent, converting the wet cellulose into alkali cellulose by the addition of a solution of caustic alkali, subjecting the alkali cellulose to the action of alkali sulfide and oxygen-containing gas, converting the alkali cellulose into cellulose xanthate, and dissolving said xanthate to form a viscose solution.

KARL K'o'ssLINGER.

ALFONS BAYERL. 

